It has now become a common practice for law enforcement, military, and emergency response personnel to utilize night vision imaging systems (NVIS) including night vision goggles (NVG) to conduct night or low-light operations. Currently, night vision imaging systems include either goggles (which are "binocular" or "monocular") which are worn by an operator, and which respond to visible and near-infrared light having wavelengths up to 930 nanometers. As is conventional, the night vision imaging systems typically generate a visible, phosphor-screen image from normally imperceptible radiation.
Typically, night vision imaging system goggles include one or two image intensifier tubes mounted to a head strap or a helmet. The image intensifier is a vacuum tube device similar to a miniature video camera and screen packaged together. Typically, the intensifier includes a photocathode receptor which receives visible light and infrared light energy and converts the visible light and infrared light energy into electrons, a microchannel plate which multiplies the number of electrons emitted by the photocathode (thus serving as an amplifying device), and a green phosphor screen which converts the electrons into a visible image. Currently, there are two types of intensifier tubes which are in widespread usage. The first type is a generation II intensifier tube, which utilizes a multialkali photocathode. The second type is a generation III intensifier tube which utilizes a more sensitive gallium arsenide photocathodes. Generation III intensifier tubes are more costly than generation II photocathode tubes, but have a longer use life.
While night vision imaging systems are very useful in law enforcement, military, and emergency response applications, they are not tolerant of high levels of visible light or infrared radiation. In other words, night vision imaging systems are best when employed in actual low light conditions.
When personnel are within a vehicle, such as, without limitation, aircraft, watercraft, or land-based vehicles, the night vision imaging systems may be useful for night operations; however, it is not uncommon for the interior space of the vehicle to include sources of visible light or infrared radiation which interfere with the operation of the night vision imaging system. High intensity visible light or high intensity infrared radiation, which is within the operating range of the night vision imaging system, impedes the effective utilization of the night vision imaging system, sometimes rendering such devices essentially useless. Consequently, illuminated displays and other sources of light which are necessary for low light operation of communication and control equipment must be neutralized in order to render night vision imaging system useful for low light operations conducted from within a vehicle. While the problem is present in all vehicles, including watercraft and land-based vehicles, it is especially acute for aircraft which are highly-instrumented devices. For example, fixed-wing aircraft or rotor-wing aircraft include a large array of gages, displays, LED devices, and the like, which emit visible light and infrared radiation which does interfere with the utilization of night vision imaging systems, such as night vision goggles.
Accordingly, in order to allow low light operations, a variety of prior art approaches have been developed for dealing with the interfering light sources within the cockpit or interior space of other vehicles such as ships, boats, and land-based vehicles.
The present invention is of generally applicability to all vehicles which may be utilized during low light operations which would benefit from the use of night vision imaging systems, and is not limited to fixed wing and rotor wing aircraft; however, for purposes of exposition only, the specification contained herein will discuss primarily fixed-wing and rotor-wing aircraft. The prior art approaches will now be discussed, with reference to fixed-wing and rotor-wing aircraft.
One approach of the prior art is to replace the dials, gages, light emitting diodes, and illuminated displays within an aircraft with comparable equipment which is illuminated within a wavelength range which would not interfere with the utilization of night vision imaging systems. One significant drawback with this prior art approach is the significant costs associated with such retrofitting operations. The costs are high because regulatory agencies such as the Federal Aviation Administration strictly require documentation of such modifications. An additional reason for the expense is that the replacement instruments have considerable costs associated with them.
A second approach of the prior art is to replace the lighting or illumination source within the instruments. This is also expensive, since it requires that the instruments, gages, and displays be individually removed and modified: Again, considerable costs are associated with the documentation required for such operations, as well as for purchase of the replacement lighting sources.
A third approach of the prior art is to install post, bezel, or flood lighting within the craft cockpit which is an alternative means of lighting the essential displays and gages. One significant advantage is that the post, bezel, or flood lighting systems are supplementary systems which do not replace the existing illumination systems within the craft. During low light operations, the lighting systems of the craft are switched from an "on" condition to an "off" condition (which is referred to as a "blackout"). The supplementary posts, bezel, or flood lighting systems are turned on and used as a sole source of illumination of the various gages, displays, meters, and the like, during the duration of the low light operations. The night vision imaging systems may be then utilized without any interference from the illumination sources associated with the cockpit instrument lighting systems.
When this approach is utilized minor/major changes to the aircraft wiring must be accommodated. This permits power to be directed to the external accessories in lieu of the original instrument.